SERIMLI MILITARY BASE, Syria (Reuters) -- Kurdish militants have trained hundreds of Yazidi volunteers at several camps inside Syria to fight Islamic State forces in Iraq, a member of the armed Kurdish YPG and a Reuters photographer who visited a training camp said on Sunday.

The photographer spend Saturday at the training camp at the Serimli military base in Qamishli, northeastern Syria on the border with Iraqi Kurdistan, where he saw 55 Yazidis being trained to fight the Islamic State.

Dressed in green military fatigues, young and old men were taught how to use assault rifles and rocket-propelled grenades by the Syrian Kurds, sweating in the 40 degree Celsius heat.

"The Yazidi civilians want to stay in Syria because it is safer but the volunteers really want to go back to Iraq to fight," he said by phone.

Iraq has been plunged into its worst violence since the peak of a sectarian civil war in 2006-2007, with Sunni fighters led by the Islamic State overrunning large parts of the west and north, forcing hundreds of thousands to flee for their lives and threatening ethnic Kurds in their autonomous province.

Thousands of Yazidis have also been trapped in searing heat on the mountain near the Syrian border. They fled there this month to escape the Islamic State, who deem Yazidis "devil worshippers". Yazidis follow an ancient faith derived from Zoroastrianism.

Some have been airlifted out by Iraq's Air Force and others fled into Syria with the help of Kurdish militants.

In Syria, the Yazidi volunteers train in weapon use and fighting tactics for several days before being sent back to Mount Sinjar to fight, a member from the media office of the Kurdish YPG told Reuters.

"There are several training camps for Yazidi men who have volunteered," Anas Hani said from eastern Syria. "In the past ten days, hundreds have graduated. And we are training more."

"On the top of the Singar mountains, in cooperation with locals and the YPG, the Yazidis have established what they call the Singar Resistance Units," he said by phone.

The YPG, or the People's Defence Units, says it has no political affiliations but analysts say it has close ties to the Kurdistan Workers Party, PKK, who have waged a guerrilla war in Turkey for decades and which the U.S. lists as a terrorist organisation.

The IS advances have drawn the first U.S. air strikes on Iraq since the withdrawal of American troops in 2011.

Iraqi Kurdish officials have sought to play down the role of the YPG in Iraq and spotlight the actions of their own peshmerga forces, who are already being supplied weapons by the United States.

Ethnic Kurds in Syria have a complex role in nearly four years of conflict that started when President Bashar al-Assad cracked down on a pro-democracy uprising.

The ensuing civil war has pitted Sunni Muslims against Assad's Alawite minority and different Kurdish militia have fought on both sides, normally over territory or power disputes.

The YPG are one of the few militant groups that have been able to stem the advance of the Islamic State, the most powerful rebel group in Syria and Iraq.